However, when I use the Sencha SDK tools to build my app for production

Code:

sencha app build production

the landing page, index.html contains the Microloader which is responsible for loading the app, checking for delta updates, loading the Sencha framework and probably many other things, but does not contain any webkit browser checking.

How could I implement this kind of checking to make sure the user is using a Webkit browser? Since we're not directly loading the Sencha framework, I can't use the above browser checking code. I guess when then code snippet is run, Sencha hasn't loaded yet, hence why I get an 'undefined' javascript error.